Inverted T-beam (Reinforced Concrete) Analysis and Design 1

[kellez]

Hi everyone,

I have already finished the design of a Reinforced Concrete ground floor house (108m2) but i want to replace one drop beam (250x500cm) with an inverted beam (600x350cm).
What is the best way to carry out the analysis in Autodesk Robot? I have already replaced the existing beam in my model with the dimensions of the inverted beam and carried out the analysis but i know this not representative.
What else shall i do before i carry out the analysis?

 

[Seppe]

Why not just run it by hand and simply represent it in the software as a dummy member?

 

[KootK]

From a modelling perspective, you simply want analysis results that are consistent with with expected member stiffness based on your anticipated detailing. Will you count on beam continuity over supports for this application? Will you account for member cracking with respect to stiffness. Stuff like that.

If you want to ignore T-beam action for sagging moments -- as most engineers likely would -- then you'll want to find a way to turn that off in your software prior to analysis and design. As Seppe intimated, this may make a hand run design the preferred approach. I'm not saying that this is a situation where you cannot use your software but, given the atypical nature of the situation, it would behoove you to take extra care in understanding how your software is approaching the design if you do.

This is a minor point but note that, by introducing the load to the beam at the bottom of the beam rather than the top, your stirrup demand will increase a bit to account for the hanger function. Software often does not account for this.

 

[kellez]

Hi and thank you for the replies.

I assume my modelling is correct.
1) i have applied releases to the two ends,
2) there is no continuity, its a single beam,
3) i have taken into consideration cracking by reducing the stiffness of the beam by 0.5Ix 0.5Iy & 0.1Iz
4) the software does not take into consideration T-beam effects

I already have the analysis results using the above model, but i guess there is nothing else i can change regarding modelling to closer represent an inverted beam.

In order to carry out the design by hand calculations what would be the main difference? I imagine the neutral axis? But lets say i am ignoring the slab effect on the beam does that mean i would carry the calculations as an ordinary beam?

 

[hoshang]

Hi,
Please find these links:

https://forums.autodesk.com/t5/robo...inverted-t-section-rc-beam-design/m-p/7072094

https://forums.autodesk.com/t5/robot-structural-analysis-forum/inverted-beam/m-p/5806438#M37437